The regulation of intake involves multiple types of interacting behavioral and physiological control mechanisms. Malfunctions in one or more of these control mechanisms are presumed to underlie disordered patterns of food intake and body weight regulation, such as those associated with obesity or anorexia. A property of food that may play a role in the maintenance of energy balance is viscosity, defined as the resistance of a substance to flow. Recent reports suggest that the ability of humans to adjust their intake to compensate for calories consumed depends, at least in part, on the viscosity of the food. The potential role of food viscosity on intake regulation has not been investigated systematically within a non-human animal model. The purpose of the proposed research is to use the control that is afforded by a rat model of appetitive and consummatory behavior to begin this investigation. Our research will assess the effects of feeding rats foods that are the same in terms of their caloric and nutritive content, but that differ in viscosity. Studies will examine both short-term and long-term effects of differences in viscosity on food intake and body weight regulation. Further, there is good reason to believe that the viscosity of human breast milk and rat milk varies over time in a manner that is directly correlated with the milk's caloric and macronutrient content. It may be that the influence of viscosity on intake regulation of both species, during the early stages of life as well as during adulthood, depends on exposure to this relationship. Thus, additional experiments will examine the sensitivity of young rats to differences in diet viscosity and the age at which such sensitivity begins to influence food intake and body weight regulation. Further, we will examine the effects of experience, both early in life and later in adulthood, with foods that differ in viscosity and calories on subsequent intake regulation by viscosity, and will examine the importance of viscosity as a signal-modulating intake (compared to other sensory signals like taste). Finally, we will explore the mechanisms that may contribute to ability of differences in the viscosity food to produce differences in the regulation of food intake. A careful examination of the role of viscosity in regulation of food intake and body weight is particularly critical given the rapid rise in overweight during the last 20 years. This rise has been accompanied by large increases in the consumption of soft drinks, fruit juices and other beverages, that are high calorie, but low viscosity. Our studies will provide us the increased control afforded by the use of non-human subjects in order to directly test the hypothesis that high calorie, low viscosity foods may compromise the ability to effectively regulate intake, and thereby may contribute to recent trends toward obesity and overweight, including dramatic increases in the prevalence of childhood obesity. [unreadable] [unreadable]